科研之友
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摘要
We present detailed images of diffuse ultraviolet (UV) intergalactic light (IGL), situated in a 60-kpc halo that surrounds the radio galaxy MRC 1138-262 at z = 2. We discuss the nature of the IGL and rule out faint cluster galaxies, nebular continuum emission, synchrotron, inverse Compton, synchrotron self-Compton emission and scattering of galactic stellar light as possible sources of the IGL. Dust-scattered quasar light is an unlikely possibility that cannot be ruled out entirely. We conclude that the source of the IGL is most likely to be a young stellar population distributed in a halo encompassing the radio and satellite galaxies, undergoing star formation at a rate greater than 57 +/- 8 M circle dot yr(-1). Within 70 kpc of the radio core, approximately 44 per cent of the star formation that is traced by UV light occurs in this diffuse mode. The average UV colour of the IGL is bluer than the average galaxy colour, and there is a trend for the IGL to become bluer with increasing radius from the radio galaxy. Both the galaxies and the IGL show a UV colour-surface brightness relation which can be obtained by variations in either stellar population age or extinction. These observations show a different, but potentially important mode of star formation, which is diffuse in nature. Star formation, as traced by UV light, occurs in two modes in the high-redshift universe: one in the usual Lyman-break galaxy clump-like mode on kpc scales, and the other in a diffuse mode over a large region surrounding massive growing galaxies. Such a mode of star formation can easily be missed by high angular resolution observations that are well suited for detecting high surface brightness compact galaxies. Extrapolating from these results, it is possible that a significant amount of star formation occurs in large extended regions within the haloes of the most massive galaxies forming at high redshift.
- 出版日期2008-1-21
